The present invention relates to an image processing apparatus and method and, more particularly, to an image processing apparatus and method, which electrically read an original image, perform image processing of the read image, and output the processed image to an external apparatus.
In recent years, as image reading apparatuses for generating an image signal by electrically reading an original image, so-called scanners have been commercially available. A conventional monochrome scanner normally uses a white plate as a pressing plate that serves as the background of an original reading unit. A case will be examined below wherein the output original image read by scanner is received and displayed by an image processing apparatus (e.g., a host computer or the like) on the output side or is temporarily stored in an external storage device, and is reproduced and displayed or printed out later. In this case, when the size of the original image is smaller than that of the display screen of a display on the host computer side or the size of a recording medium or the like used for printing out the image, the boundary between the original image and the background cannot be recognized, as shown in, e.g., FIG. 2D, and hence, an accurate original size cannot often be determined. This is because both the background color of the original and the pressing plate are white. On the other hand, character images and the like in the original image appear to float in the air with respect to the background, and the image position cannot be discriminated, resulting in image information which is not easy to see.
In order to solve such problems, the following method has been proposed. That is, in the conventional scanner, the background of the original reading unit is painted black, and an original image 201 is read by adding a black background 202 thereto, as shown in FIG. 2A. With this method, the size information of the original image can be provided upon reading an image, and hence, this means is effective for solving the above-mentioned problems.
In this case, no problem is posed when the original image is displayed on the display of the host computer, as described above. However, when the read image is to be printed out, the following problems are posed. That is, since the solid black portion added around the original image is printed out as it is, a recording agent such as ink, toner, or the like of a printer apparatus is consumed in large quantity, and at the same time, unwanted ink or toner scattering frequently occurs inside the apparatus, thus considerably contaminating the respective members.
In order to solve the new problem, the following method (image frame addition processing) has been proposed. That is, when an image read by the scanner is printed out, a software program on the host computer side detects the boundary line portion between the original image and the surrounding black background portion, and converts the color of a portion other than a thin line portion of the surrounding portion to match the foundation color of the original. With this method, the image on which only the original size information is left as a thin-line image frame can be output to the printer apparatus.
However, since the image frame addition processing in the conventional scanner is realized by software, it is normally considerably low-speed processing, thus requiring a long time for printing out the image. Since not all application programs, which run on the host computer and use the scanner, always support the above-mentioned image frame addition function, the image frame addition processing cannot be versatilely applied to all the application programs that use the scanner.
Therefore, in order to solve the above-mentioned problems in the conventional scanner, it is effective to add a hardware image frame addition means which performs sequential processing equivalent to the above-mentioned software processing in synchronism with the reading operation of the original image, i.e., in synchronism with the transfer clocks of pixel data.
A case will be examined below wherein an image frame addition circuit that can attain high-speed sequential processing is arranged in the scanner, and is operated all the time. Assume that an original image 301 having a halftone (e.g., red) foundation portion 303 in a portion contacting a surrounding portion (black region) 302 of the original image, as shown in, e.g., FIG. 3A, is to be processed. In this case, the image frame addition circuit erroneously recognizes the halftone region (red region) 303 contacting the surrounding portion of the original image as the background portion 302. As a result, the halftone region is erroneously converted into a white region upon printing out, and a strange image different from the original image 301 is transmitted to the host computer side, as shown in FIGS. 3C and 3D.
In order to avoid such problem, it is, of course, possible to add a means for manually bypassing the image frame processing function to the scanner. In this case, the operator checks the original image, and can disable the image frame processing function in advance when the above-mentioned original image is to be read.
However, the method of manually bypassing the image frame processing function is effective for a flat-bed scanner which can start reading after the operator sets an original image one by one on the scanner. However, when an ADF (auto document feeder) unit is added to the flat-bed scanner, or a sheet-through (original feed type) scanner which reads an original image by separating an original image one by one from a stack of a plurality of original images and successively feeding the original images, or the like is used, it is difficult for the operator to check each original image, and hence, the above-mentioned method cannot be an effective solution.